This application is a continuation-in-part application of U.S. patent application Ser. No. 09/298,859, filed Apr. 26, 1999.
(1) Field of the Invention
This invention relates to integrated circuit package, in particular to multiple chip module (MCM) package.
(2) Description of the Related Art
As memory capacity of an integrated circuit chip increases from 4M, 16M, 64M, 128M to 256M, the manufacturing difficulty also increases and the manufacturing yield decreases. Another approach in increasing the memory capacity is to improve the packaging technique. For instance, a 128M memory can be obtained by packaging two 64M chips in one package, known as Multi-chip Module (MCM). In this manner, the yield can be increased and the manufacturing difficulty can be reduced.
Another popular packaging technique is the micro Ball Grid Array (.mu.BGA) package. FIG. 1A shows the use of .mu.BGA for a single IC chip 10. The IC chip 10 has bonding pads 12 along the periphery which are lead-bonded through bonding wires 16 to the bottom of substrate 14, as shown in FIG. 1B. The IC chip 10 is separated from the substrate 14 by a resin 15, which serves to cushion the difference in thermal expansion of the IC chip 10 and the substrate 14. The substrate 14 has ball grid array 18 at the bottom of the substrate 14 for surface mounting to a printed circuit board.
The structure shown in FIGS. 1A and 1B does not have provision to dissipate the heat generated in IC chip 10 because the resin 15 is a poor heat conductor. The problem is more serious for modern VLSI IC chip where large amount of heat may be generated.
Another limitation to packing density of the present-day structures is that the printed circuit wiring of the substrate for the .mu.BGA is single-sided. Thus, the interconnection pattern is limited.